Photoreceptor interface

ABSTRACT

AN ORGANIC INTERFACE SUITABLE FOR USE WITH A PHOTOCONDUCTIVE INSULATING LAYER, SAID INTERFACE COMPRISING A POLYMER BLEND OR MIXTURE OF POLYCARBONATE AND POLYURETHANE RESINS. THE INTERFACE OR BLOCKING LAYER IS NORMALLY USED AS A LAYER WHICH IS SANDWICHED BETWEEN A PHOTOCONDUCTIVE INSULATING LAYER AND A SUPPORTING SUBSTRATE. THE INTERFACE COMPOSITION EXHIBITS OUTSTANDING MECHANICAL PROPERTIES AND ELECTRICAL CHARACTERISTICS.

Jan. 30, 1973 D. J. ANGELINI 3,713,821

PHOTORECEPTOR INTERFACE Filed June 10, 1971 INVENTOR DOMINIC J. ANGELINI A 7' TORNEY United States Patent 3,713,821 PHOTORECEPTOR INTERFACE Dominic J. Angelini, Webster, N.Y., assignor to Xerox Corporation, Stamford, Conn. Filed June 10, 1971, Ser. No. 151,659 lint. Cl. (303g 5/10, 5/00 U.S. Cl. 96-].5 17 Claims ABSTRACT OF THE DISCLOSURE Bushman BACKGROUND OF THE INVENTION This invention relates in general to xerography, and in particular, to an improved interfacial layer for a xerographic member.

In the art of xerography, a xerographic plate containing a photoconducting insulating layer is first given a uniform electrostatic charge in order to sensitize its surface. The plate is then exposed to an image of activating electromagnetic radiation, such as light, which selectively dissipates the charge in the illuminated areas of the photoconductive insulator while leaving behind a latent electrostatic image in the nonilluminated areas. The latent electrostatic image may be developed and made visible by deposited finely divided electroscopic marking particles on the surface of the photoconductive layer. This concept was originally described by Carlson in US. Pat. 2,297,691 and is further amplified and described by many related patents in the field.

Conventionally, a xerographic member or plate normally includes a conductive base or support which is generally characterized by the ability to conduct electricity for charging or sensitization of a composite member and to accommodate the release of electric charge upon exposure of the member to activating radiation such as light. Generally, this conductive support must have a specific resistivity of less than about ohm-cm, and usually less than about 10 ohm-cm. The conductive support should also have sufiicient structural strength to provide mechanical support for the photosensitive member thus making it readily adaptable for xerographic machines suitable for commercial use.

The conventional xerographic plate normally has a photoconductive insulating layer overlaying a conductive support. The photoconductor may comprise any suitable material known in the art. For example, vitreous selenium, or selenium modified with varying amounts of arsenic is one example of one suitable reusable photoconductor which has Wide use in commercial xerography. In general, the photoconductive layer must have a specific resistivity greater than about 10 ohm-cm. in the absence of illumination and preferably at least 10 ohm-cm. The resistivity should drop at least several orders of magnitude in the presence of activating radiation or light. In general, the photoconductive layer should support an electrical potential of at least about 100 volts in the absence of radiation and may vary in thickness from about 10 to 200 microns.

A plate having the above configuration, normally under dark room conditions, exhibits a reduction in potential or voltage leak in the absence of activating radiation which is known as dark decay and exhibits a variation in electrical performance upon repetitive cycling which is described in the art as fatigue. The problem of dark decay and fatigue are well known in the art and have been remedied by the incorporation in the plate structure of a barrier layer which comprises a thin dielectric material only a fraction of the thickness of the photoconductive layer. This barrier or interfacial layer is inter-disposed between the conductive substrate and the photoconductive insulating layer. US. Pat. 2,901,348 to Dessauer et al. contemplates such a layer-and suggests the use of a thin layer or film of aluminum oxide in a thickness range of about 25 to 200 angstroms; or an insulating resin layer, such as polystyrene, in the order to about 0.1 to 2 microns in thickness. These barrier layers function to allow the photoconductive layer to support a charge of high field strength with minimum charge dissipation in the absence of illumination. When activated by illumination, the photoconductive layer becomes conductive, thereby causing a migration of the appropriate charges through said photoconductive layer and the appropriate dissipation of charge in the radiation or illumination struck areas.

In addition to the electrical requirements of a barrier layer, it is also necessary that such a layer meet certain requirements with regard to mechanical properties such as photoreceptor adhesion and overall flexibility. For example, when using a flexible photoreceptor, such as a continuous belt, both the photoconductor and interface must be properly matched so as to have the required electrical characteristics and mechanical stability. It has been demonstrated that after a great deal of flexing, many interfaces tend to spall or crack, resulting in the flaking off or spalling of sections of the photoreceptor rendering it no longer suitable for use in xerography. Therefore, there is a continuing need for improved barrier layers which meet both the required electrical characteristics and mechanical properties for use in applications in which a flexible xerographic member or belt is used.

OBJECTS OF THE INVENTION It is, therefore, an object of the invention to provide a new and improved photoreceptor barrier layer which overcomes the above noted disadvantages.

It is another object of this invention to provide a photoreceptive member which exhibits outstanding electrical characteristics and mechanical properties.

It is another object of this invention to provide an improved interfacial barrier layer.

SUMMARY OF THE INVENTION The foregoing objects and others are accomplished in accordance with this invention by providing a photoconductive member which exhibits outstanding electrical characteristics and mechanical properties, and which includes a novel interfacial barrier layer which comprises a polycarbonate and polyurethane resin. More specifically, the interfacial layer comprises either a polymer blend or mixture of a polycarbonate and a polyurethane which is sandwiched between a photoconductive insulating layer and a supporting substrate. One of the advantages of this innterfacial composition is that it exhibits outstanding tensile strength, elongation, modulus of elasticity, adhesive properties, and electrical characteristics which far exceed the properties of the individual polycarbonate or polyurethane resins separately.

BRIEF DESCRIPTION OF THE DRAWING The advantages of the instant invention will become apparent upon consideration of the following disclosure of the invention, especially when taken in conjunction with the accompanying drawing wherein:

The figure represents a schematic illustration of one embodiment of a xerographic member as contemplated for use in the instant invention.

3 DETAILED DESCRIPTION OF THE DRAWINGS In the drawing, reference character 10 illustrates one embodiment of an improved photoreceptor device of the instant device. Reference character 11 designates a support member which is preferably an electrically conductive material. The support may comprise a conventional metal such as brass, aluminum, steel, or the like. The support may also be of any convenient thickness, rigid or flexible and in any suitable form such as a sheet, web, cylinder, or the like. The support may comprise other materials such as metalized paper, plastic sheets covered with a thin coating of aluminum or copper iodide, or glass coated with a thin conductive layer of chromium or tin oxide. A preferred substrate for use in the instant invention comprises an endless flexible seamless xerographic belt which comprises nickel, and which is formed by the method described in applicants co-pending application, Ser. No. 7,289 filed on Jan. 30, 1970.

The substrate 11 is overlayed with an organic interfacial layer 12, which comprises a polymer blend or mixture of a polycarbonate and a polyurethane resin. In general, the ratio by weight of the polycarbonate to polyurethane resin should be kept within about 1 to 1 and 7 to l. Polyurethane concentrations of less than 13 percent by weight (7 to 1 ratio) do not have mechanical properties suitable for use in the instant invention, while concentrations of polyurethane over about 50 percent by weight are undesirable in that high concentrations of polyurethane present fabrication or coating problems. Although high molecular weight polycarbonates (casting resins) are preferred (those having a molecular weight averaging of from about 75,000 to 100,000) any suitable polycarbonate resin may be used. The polyurethane resins are of the type referred to as saturated, thermoplastic, polyester-based.

Typical polycarbonates suitable for use in the instant invention comprise Makrolon 75052, and Makrolon 9005Z, available from Bayer Dyestuffs and Chemicals Ltd.; Merlon M50 Natural, Merlin MSG-1010 Clear Tint, and Merlon 1,000 pdr, all available from Mobay Chemical Company; Lexan 125 and Lexan 155, available from General Electric Co., Chemical Materials Dept.

The typical polyurethane resins suitable for use in the instant invention include Vithane TPU123, available from Goodyear Tire and Rubber Co., Chemical Division; and Estane 5703, available from B. F. Goodrich Chemical Com any.

The interfacial layer may be made by any convenient technique. For example, the appropriate proportions of polycarbonate and polyurethane resins are normally dissolved in a solvent and the resin solution coated onto a supporting substrate. The solvent is then allowed to evaporate leaving a fla h dried coating contained on the supporting substrate. Residual solvents are then driven off by oven drying at 150 to 300 F. for about minutes. Typical coating techniques which are suitable for forming the interfacial layer include spray coating, draw coating, dip coating, or flow coating. In general, the dried thickness of the interfacial layer should be about 0.5 to i 3.0 microns. Thicknesses less than about 0.5 micron are undesirable in that they do not give a uniformly thick layer, are porous and do not uniformly cover substrate roughness. In addition, they are difiicult to charge and tend to leak electrical charge. Thicknesses above about 3.0 microns result in non-charge dissipation. In general, the composite resistivity of interfacial layer ranges from about to 10 ohm-cm.

In addition to the above polycarbonate and polyure-v thane resins, other additives may be added to the mixture.

These additives include small amounts of conductive or photoconductive pigments such as copper phthalocyanine, zinc oxide (electrography grade), cadmium sulfoselenide, and metal-free phthalocyanine. In general these additives a e u ed to co trol. the resistivi y of he int rfacial barrier layer, and in some cases are even believed to improve the mechanical properties of the layer.

Although the exact structure of the interface has not been clearly defined, at low concentrations of polyurethane, in the range of about 13 weight percent to 35 weight percent, the structure of the interfacial layer appears to comprise a polyblend of spherical polyurethane particles contained in a surrounding polycarbonate matrix. The size of the spherical polyethylene phase or particles appears to increase with an increase in concentration of the polyurethane. At concentrations in the vicinity of 35 to 50 Weight percent, it is believed that a coalescence or flowing together of the dispersed particles results.

A preferred application of the instant invention includes the use of the instant interface on a flexible endless belt which may typically comprise a conductive material such as nickel or brass. In addition to the required electrical characteristics, it is essential that the interfacial layer of the instant invention have a high degree of flexibility and forms a satisfactory adhesive and cohesive interface between the photoconductive layer and the supporting substrate.

Photoconductive insulating layer 13 overlays interfacial layer 12. The photoconductor may comprise any suitable photoconductive insulator which is compatible with the insulating resins and forms an adherent layer which properly bonds the photoconductive layer to the substrate. Suitable photoconductive materials include vitreous selenium or selenium alloyed with materials such as arsensic, antimony, tellurium, sulfur, bismuth and mixtures thereof. A preferred photoconductor comprises a vitreous alloy of selenium containing arsenic in an amount from about 0.1 to 50 percent by weight. The thickness of the photoreceptor layer is not particularly critical and may range from about 10 to 200 microns. In general, thicknesses in the range from about 20 to microns are particularly satisfactory for use in conventional xerography. The photoreceptor layer may be prepared by any suitable technique. A preferred technique includes vacuum evaporation wherein the appropriate material or alloy is evaorated over the interfacial layer. In general, a selenium or selenium-arsenic alloy layer thickness of about 60 microns is obtained when vacuum evaporated is continued for about 1 hour at a vacuum of 10- torr at a crucible temperature of about 280 C. U.S. Pats. 2,803,542 to Ullrich, 2,822,300 to Mayer et 211., 2,901,348 to Dessauer et a1. and 2,753,278 to Bixby all illustrating vacuum evaporation techniques which are suitable in the formation of selenium or selenium alloy layers of the instant invention.

In order to gain added sensitivity when using seleniumarsenic layers, a halogen dopant such as chlorine or iodine, may be added in order to improve the electrical characteristics. This concept is more fully described by US. Pat. 3,312,548 to Straughan.

DESCRIPTiON OF THE PREFERRED EMBODIMENTS The following examples further specifically define the present invention with respect to a method of making a photoreceptor member having an interfacial barrier layer. The percentages in this specification, examples and claims are by weight unless otherwise stated. The examples below are intended to illustrate various preferred embodiments of the instant invention.

EXAMPLE 1 A coating solution for forming an organic inter-facial barrier layer is prepared as follows: 76.8 grams of polycarbonate resin (Merlon M50, available from Mobay Chem. Co.) is dissolved in 1280 milliliters of ethylene dichloride solvent. A second solution is made containing 16 grams of copper phthalocyanine (available from Hercules Inc., Imperial Department) dispersed in 1540 milliliters of p-dioxane solvent. A third solution is made com prising 19.2 grams of polyurethane resin (TPU 123 available from Goodyear Tire and Rubber Co., Chemical Division) diluted in 6-25 milliliters of cyclohexanone solvent. The copper phthalocyanine pigment is added to the dioxane solvent and stirred together, this solution then added to the ethylene dichloride-polycarbonate solution. This solution is milled in a pebble mill jar for 16 hours.

The polyurethane resin is dissolved in the cyclohexanone solvent, filtered one pass through a Sethco recirculating cartridge filter, one pass through a Gelman 0.2 micron absolute filter, then added to and mixed with the polycarbonate-copper phthalocyanine solution. Tetrachloroethylene solvent is then added to the above mixture to control the solution viscosity and drying rate for spraying. This mixture is then coated onto a continuous flexible nickel belt .0045 inch thick, approximately 16 /2 inches Wide and 65 inches in circumference by spray coating using an air atomized spray process with a Binks electrostatic spray gun. The coating is then allowed to dry, as described previously, to form a thickness of about 1.5 microns. This results in the formation of an interfacial layer which contains a ratio of 4 parts by Weight polycarbonate resin to 1 part by weight of polyurethane resin, and about 14 weight percent copper phthalocyanine.

The coated nickel substrate is then mounted onto a Type Poly-poly 4:1 (270 F.). Poly-poly 8:1 (270 F.)

selenium-3% arsenic and the interface layers are about 1 to 2 microns in thickness.

Each of belts 1-21 are tested under three conditions as follows:

Cold test-The flexible coated photoreceptor belts are mounted over 'two five-inch cardboard inserts and placed in a storage box and held at -20 F. for four hours. To pass the test, the photoconductor coating must remain intact without cracking or spalling.

Shock test.The photoreceptor belts, While still in a storage box, are dropped from a 42" height onto a supporting floor. To pass the test the photoreceptor layer must remain intact and the belt substantially undamaged.

Flex test.-Each belt is then mounted on a tri-roller assembly adapted to rotate the belt over each roller. ambient temperature is 110 F. and the belts are cycled for 1000 cycles in minutes and then rested for five minutes. This test is repeated for 30,000 cycles unless the belt fails before the end of 30,000 cycles. To pass the test the belt must complete 30,000 cycles without exhibiting cracks which are visible to the eye.

Each of belts 121, made by Examples I-XXI are tested under the conditions of the three tests described above and the results tabulated in the following table.

Do. Failed at 7K Passed 7K.

Failed in 9K.

do.. Passed.

(1 Failed.

Passed. Do. Do. Do. do Do.

Polyester (100%) (270 F.) Failed at 17 K. d0 Failed at 21 K.

Estane 5703 (100% polyurethane) 270 F Failed- Passed (in do do Ftkiled at 3-4 jn fin (in do do do Failed at 51K.

Polycarbonate (100%) 270 F Failed. do Failed Passed.

1 Poly-poly represents the weight ratio of polycarbonate to polyurethane. 2 K represents thousands of cycles.

circular mandrel and inserted in a vacuum chamber. An alloy source containing about 99.67 Weight percent selenium and 33% weight percent arsenic and containing 30 parts per million chlorine, is inserted in a stainless steel crucible beneath the coated nickel substrate. During vacuum evaporation the substrate is rotated about its longitudinal axis at a rate of about 6 to 12 revolutions per minute. The vacuum chamber is evacuated to a vacuum of about 5 l0 torr. The crucible containing the selenium-arsenic alloy is then heated to a temperature of about 300 C. and evaporation continued for about minutes resulting in vitreous selenium-arsenic alloy photoreceptor being coated over the interfacial layer in a thickness of about 60 microns. At the end of this time, the vacuum chamber is cooled to room temperature, and the vacuum broken, and the composite flexible photoreceptor belt removed from the chamber.

EXAMPLES II-XXI Twenty additional coated flexile nickel belts are prepared by themethod of Example I containing various types of resin interfaces. These belts are designated belts 2-21 respectively. Belts 2 through 13 contain various ratios of polycarbonate to polyurethane: Belts 14 and 15 comprise a 100% polyester interface; belts 16, 17, 18 and 19 contain 100% polyurethane interfacial layers; While belts 20 and 21 contain 86 weight percent polycarbonate and 14 weight percent copper phthalocyanine. The photo- Where a blank exists for a test for a given belt, it should be understood that the particular test was not conducted. The temperature listed for each belt is that which is used to dry off the residual solvent. It can be seen from the results set forth in the table that those belts containing the p0lycarbonate-polyurethane interfaces falling within the ratio set forth in the specification, passed all of the three tests Without failure. These are belts 1, 9, 10, 11, 12 and 13. Belts 2, 3, 4, 5, 6, 7 and 8, which are at the minimum concentration for the polyurethane, exhibit marginal properties in that three of the seven belts failed to pass the flex test. Belts 14 and 15, which are made of a polyester resin, illustrate that single organic materials normally do not exhibit outstanding properties, and both failed the flex test. Belts 16, 17, 18 and 19, which comprise 100 percent polyurethane do not exhibit outstanding properties in that all four belts failed the cold test. In addition, belts 17 and 19 also failed the flex test. Belts 20 and 21, which comprise only the polycarbonate resin which contains about 14 weight percent copper phthalocyanine, either failed the flex test or the cold test. Polycarbonate alone is not suitable for use as a barrier layer in that its resistivity of 10 ohm-cm. is too insulating.

Although specific components and proportions have been stated above in the above description of the preferred embodiments of this invention, other suitable procedures and materials such as those listed above, may also conductive layer is a 60 micron layer of about 99.7% be used with similar results.

Other modifications and ramifications of the present invention would appear to those skilled in the art upon reading the disclosure. These are also intended to be within the scope of this invention.

What is claimed is:

1. A xerographic member which comprises a conductive substrate having thereon an interfacial barrier layer having a thickness of about 0.5 to 3.0 microns, said barrier layer comprising a polymer blend or mixture of a polycarbonate and polyurethane resin in a ratio of about 7 to 1 parts by weight polycarbonate to 1 part by weight polyurethane,,and a photoconductive layer about to 200 microns in thickness overlaying said interfacial layer.

2. The member of claim 1 in which the photoconductor comprises a vitreous alloy of selenium and arsenic.

3. The member of claim 1 in which the arsenic is present in an amount of about 0.1 to about 50 percent by weight, with the balance substantially selenium.

4. The member of claim 1 in which the composition of the barrier layer further includes a phthalocyanine.

5. The member of claim 4 in which the phthalocyanine is selected from the group consisting of copper phthalocyanine and metal-free phthalocyanine.

6. A photoreceptor member comprising a conductive substrate having thereon an interfacial barrier layer having a thickness of about 0.5 to 3.0 microns comprising a polymer blend or mixture of 50 to 87 weight percent polycarbonate and 13 to 50 percent by weight of a polyurethane resin, a photoconductive layer about 10 to 200 microns thick overlaying the interfacial layer, said photoconductive layer comprising a vitreous alloy of selenium containing arsenic in the range of about 0.1 to 50 percent by weight, with the balance substantially selenium.

7. The member of claim 6 in which the photoconductive layer comprises about 99.67 weight percent selenium and 0.33 weight percent arsenic.

8. The member of claim 7 in which the seleniumarsenic photoconductor contains a chlorine dopant.

9. The member of claim 6 in which the photoconductive layer comprises vitreous selenium.

10. The member of claim 6 in which the photoreceptor member is in the form of a endless flexible belt.

11. The member of claim 10 in which the flexible belt substrate is made of nickel.

12. The member of claim 11 in which the photoreceptor comprises about 99.67 weight percent selenium and 0.33 weight percent arsenic.

13. The member of claim 12 in which the seleniumarsenic photoconductor contains a chlorine dopant.

14. The member of claim 10 in which the belt substrate is made of brass.

15. The member of claim 10 in which the belt substrate is made of a material selected from the group which consists of nickel, brass, aluminum and stainless steel.

16. The member of claim 6 in which the composition of the barrier layer further includes a phthalocyanine.

17. The member of claim 16 in which phthalocyanine is selected from the group consisting of copper phthalocyanine and metal-free phthalocyanine.

References Cited UNITED STATES PATENTS 3,573,906 4/1971 Goffe 96-15 X 3,312,548 4/1967 Straughan 961.5 2,901,348 8/1959 1 Dessauer et al 9'6-1 R 3,155,503 11/1964 Cassiers et al. 961.5 3,243,293 3/1966 Stockdale 961.5 3,554,742 '1/1971 Gramza et al. 96--1.5 3,403,019 9/1968 Stably et al. 96--1.5 3,431,224 3/1969 Goldblum 260'-858 X CHARLES E. VAN HORN, Primary Examiner US. Cl. X.R. 

